Black Holes–the name conveys sinister mystery. Although first suggested in 1783 (by John Michell [sic]), their existence has only been confirmed in recent years. They pose a conundrum for Einstein's Relativity Theories. According to conventional wisdom Black Holes are so dense that their mass is squeezed to zero volume–a
singularity. Two infinities–zero volume, infinite density. Two impossibilities, according to conventional wisdom. (Although, this same conventional wisdom also believes the
Big Bang began with a singularity.) So Einstein was wrong and Relativity must go.
But wait! Here comes String Theory to the rescue. What we need is a Quantum Theory of gravity. But String Theory does not answer the conundrum–it just gets everything tied up in a terrible tangle. [READ MORE: String Theory Unraveled.]
But wait! Here comes Chris Crawford to the rescue. He is another wide-eyed, arm-chair, amateur astro-physicist. He has found another way to skin Schrödinger's cat. He will shine some light on the black-hole enigma.
Stars, like most things in the Universe, go through life cycles. The reason a star goes through phases is to maintain hydrostatic equilibrium, which is a tug-of-war between gravity and gas pressure–
ideal gas pressure during the star's life and degenerate gas pressure after the star has died. Gravity tries to squeeze the star into a very small volume. Ideal (normal) gas pressure tries to expand the star; while degenerate gas pressure resists further contraction of the star.
A star's life begins when a cloud of mostly Hydrogen gas begins to coalesce under the influence of gravity. As it contracts it heats up. If it is large enough, then eventually the temperature rises to the point where thermo-nuclear reactions begin. The nuclear reactions convert Hydrogen to Helium. When the star runs out of Hydrogen, it shrinks further and the temperature raises some more. If the star is massive enough, then the temperature raises to a point where nuclear reactions convert Helium to more complex (
higher) elements, such as Carbon, Oxygen, Neon, Silicon.
This process continues until either (1) the mass is not great enough to raise the temperature to the point where the next stage of nuclear reactions can begin; or (2) the element Iron is reached, at which point the star explodes in a catastrophic super-nova. In the first case, the star expels its outer gas shell as what is called a
planetary nebula (a spherical gass cloud which looks like a giant ring). In the second case, the star is ripped apart by a super-nova–the most violent explosion known.
There are three end-states for a star: White Dwarf, Neutron Star, Black Hole. We need to explore the first two so you can understand my thinking about the third. The end state is determined like everything else–by the mass of the remnant core of the star. A smaller mass core (< 1.44 Msun) becomes a White Dwarf. A medium mass core (between 1.44 and 3 Msun) becomes a Neutron Star. And a larger mass core (> 3 Msun) becomes what is known as a Black Hole. [Msun is shorthand for
mass of the Sun.]
In 1930 (at the age of 19), Subrahmanyan Chandrasekhar (aka, Chandra) developed the theory for White-Dwarf stars while traveling by ship from India to England for post-graduate studies. His theory has been accepted as fact. White Dwarfs had been known as peculiar stars–small, dim stars emitting white light. Chandra showed that these stars are not normal main sequence stars, but rather the glowing remains of once active stars. The light they emit is not generated by nuclear reaction; rather it comes from thermal radiation (heat) produced by gravitational compression.
White Dwarfs have the mass of the Sun, but they are only the size of the Earth. They are very dense–much more dense than normal stars. They achieve this density because they are made of degenerate matter–atoms in which the electrons have been separated from the nucleus. Without the electron cloud swarming around the nucleus, there is nothing to keep the nuclei apart from each other. Gravity squeezes the nuclei together so tightly that they form a lattice-like structure. The gravity is so strong that White Dwarfs with larger mass actually have a smaller size. A degenerate gas of electrons keeps the star from collapsing completely.
In 1967 (at the age of 24), Jocelyn Bell (full married name: Susan Jocelyn Bell Burnell) discovered rapid-but-regular radio-frequency pulsations while searching for quasars as a graduate student in England. The source was first named
LGM-1 (Little Green Men), because the signal pulse was so regular that it could have come from a radio beacon of an alien civilization.
Later, it was determined that the source was a pulsar and that there were a lot more of them in the sky. Study revealed that pulsars are rapidly spinning stars with a strong magnetic field, which emit an electromagnetic pulse each revolution. Because the pulses are so rapid, pulsars must be very small and dense. (A larger body would be ripped apart by centripetal force.)
Further analysis discovered that pulsars are actually Neutron Stars. The mass of Neutron Stars is about 1-1/2 Msun, but their diameter is only about 6 miles. So their density is much, much greater than White Dwarfs. Neutron Stars are almost all neutrons. (The escape velocity from a Neutron Star is 20% of the speed of light–so strong that it bends light enough to see two-thirds of the surface, including some of the far side of the star.) The gravity is so strong that protons and electrons combine to form neutrons. Since neutrons have no electrical charge to keep them apart, the nucleus of atoms collapses into a mass of neutrons with no space between them. The neutrons form a super-fluid, degenerate gas, which stops the gravitational contraction.
In 2005 (at the age of 63), Christopher Crawford, a semi-senile old man who does not know what day of the week it is, while contemplating the lint in his navel, proposed a new model for Black Holes, which builds on the structural changes which occur in White Dwarfs and Neutron Stars. Neutrons are composed of three quarks. Theory says that at the density of one billion electron volts per cubic fentometer (1 fm = 10-15 meter) the quarks should begin to break free of the neutrons and form a sea of quarks (aka,
quark soup). (That's 1800 trillion gm/cc and denser than a Neutron Star.)
This is a field of active study with particle super-colliders. So far the experimental results are not exactly the same as theory would forecast. For example, the quarks seem to act more like a liquid than a gas. (Can anyone say degenerate matter??) Scientists observe a fireball of quarks fleeing the point of collision at relativistic speeds (half the speed of light). The quarks quickly cool and form neutrons because of the intense field of the strong force.
The new model for a Black Hole has a larger stellar remnant core reach an equilibrium point where gravity is trying to crush the core into zero volume and infinite density and where the strong force is trying to confine quarks into neutrons. This core is more massive but smaller and denser than a Neutron Star–but more than zero volume and less than infinite density. It is not hard to imagine that the escape velocity of this tiny, dense core is more than the speed of light. So there you have the model of a more massive stellar remnant core at equilibrium between the force of gravity trying to create a super-fluid degenerate gas of quarks and the strong force trying to create neutrons out of the same quarks.
Actually, we have killed two birds with one stone. Not only have we defended Einstein’s honor, but we have also found the location of the hypothetical Quark Star, which has been the subject of speculation but never observed. It never will be directly seen because it is hiding inside a Black Hole, according to this new theory.
Now, let's take on the super-massive Black Holes with the mass of millions of suns, which are believed to exist at the center of most galaxies. Oops, my brain just got . sucked . . into . . . a . . . . si.n..g...u....l.....a......r.......i........t.........y
Pop! Crack!! Snap!!!!
Where am I?
Everything looks strange!
Nothing seems normal!!
Have I been transported to a mirror-image Universe??
Ok....I think I have regained control of my intellectual functions....
There are two classes of Black Holes: solar-mass BHs (mass several times Msun) and super-massive BHs (mass of millions of Msun). Probably there is no clear-cut separation between these two classes–they are just different sides of a wide range of BH masses. Solar-mass BHs are Quark Stars; they contain matter (quarks) and occupy some volume. Super-massive BHs are true Black Holes; they have tremendous gravity because of the mass equivalence of their incredible energy (E = m × c²); but they have no volume because they have no matter. All the matter has been converted to energy in the form of photons and gluons (
energy gas), because of the unbelievable pressure and temperature at the center of the BH. Since volume is a property of matter, not energy, super-massive BHs have no volume. They could be called
I would even go so far as to say that super-massive BHs produce the unification of the strong and electro-weak forces. I leave it to the quantum physicists to calculate how much energy each one of the
strong-electro-weak force carriers contains or transmits. (Probably a lot–giga electron volts.) I am too exhausted to continue....